Our prior work indicates that women with premenstrual dysphoric disorder (PMDD) may be more vulnerable to dysphoric mood states induced by changes in gonadal hormones and their neuroactive metabolites, and not resulting from absolute levels per se. One objective of the proposed research is to determine if a continuous oral contraceptive (OC) regimen that eliminates the pill free interval (PFI) and produces stable, low endogenous hormone levels will prevent the expression of PMDD symptoms. A second objective is to demonstrate that changing hormones trigger affective symptoms in PMDD, and to establish which gonadal hormones and their neuroactive metabolites are associated with symptoms. Eighty one women with prospectively confirmed PMDD will be randomized and complete one of three, 13 week treatment arms: Treatment #1) continuous administration of 20 ug ethinyl estradiol/3mg drospirenone [EE/P];Treatment #2) interrupted EE/P, substituting placebo for EE/DRP during weeks 4, 8, &12;Treatment #3) continuous placebo. The primary outcome measure will be the total PMDD symptom score assessed daily at baseline and throughout the treatments. Secondary measures will include Response Rate, mood and social adjustment scales. Serum levels of estradiol (E2) and P, as well as plasma levels of neuroactive steroids, allopregnanolone, allotetrahydroDOC, pregnanolone and pregnenolone sulfate, all potent modulators of the GABAA receptor will be sampled on cycle days 17, 21, 25, 2, &5 at pretreatment and also during treatment month 3. Primary predictions are: 1) Continuous EE/P (arm #1) will be associated with a significant reduction in PMDD symptoms relative to pretreatment levels, and will be associated with lower symptom levels in months 2 and 3 of treatment relative to both placebo and interrupted EE/P (arms #2 and #3);2) Women treated with interrupted OC (arm #2) will show symptom severity similar to women treated with placebo (arm #3), and will continue to show cyclicity of symptoms though there will be a shift in peak symptoms to the follicular phase, corresponding primarily to the changes in E2 induced during the PFI;3) the increase in E2 during the PFI in women treated with interrupted OC (arm #2) will predict the development and severity of symptoms in that group;and 4) since OCs suppress the synthesis of neurosteroids, the magnitude of the change in neuroactive steroids from days 17 - 25 to days 2- 5 will predict PMDD symptoms in the placebo group, but not in the women treated with OCs (arms #1 and #2). The results of this study are expected to advance our knowledge on the pathophysiology of PMDD and help illuminate a substrate for affective dysregulation in women. Confirmation of the role of hormonal change in precipitating PMDD will suggest therapeutic targets for future research.